2H-1,2-Thiaborin: A New Boron–Sulfur Heterocycle

Abstract

The reaction of 2,5-dihydro-2-diisopropylamino-1,2-thiaborole (5) with 2 equiv of LDA followed by CH2Cl2 gives 2-(diisopropylamino)-2H-1,2-thiaborin (2c), which has been spectroscopically and structurally characterized. DFT calculations indicate that formally aromatic 2c has a limited π-delocalized bonding in its heterocyclic ring.

Expedient Synthesis of 1,2‐Thiaborines by Means of Sulfur Insertion into Boroles

“…Subsequent work‐up allowed the isolation of the product in 44 % yield, the identity of which was determined to be 1,2‐thiaborine 6 using X‐ray diffraction analysis. Interestingly, the 11 B{ 1 H} NMR signal is significantly different than the documented shift of the diisopropylamino species 3 (35.8 ppm), suggesting a different electronic structure. With B‐phenyl and C‐phenyl adjacent to sulfur in 6 , it could not be determined if disorder was present in the solid‐state structure; therefore, the B‐biphenyl borole 5 was reacted with S 8 to prepare a derivative that would differentiate these two positions and permit the accurate analysis of the bonding.…”

“…Fewer advances have been made for the third row; in fact, the first 1,2‐phosphaborine C was reported only last year . For sulfur, the reported derivatives are limited to two fused polycyclic systems, specifically phenanthrene analogues ( 1 and 2 ) and only a singular example of a 1,2‐thiaborine exists, reported by Ashe ( 3 ) . The synthetic methodology to prepare 3 involved a carbenoid insertion into a 1,2‐thiaborole, generating the 1,2‐thiaborine in relatively low yields .…”

“…[19] For sulfur, the reported derivatives are limited to two fused polycyclic systems, specifically phenanthrene analogues (1 and 2)a nd only as ingular example of a1 ,2-thiaborinee xists, reported by Ashe (3). [14,20,21] The synthetic methodology to prepare 3 involved ac arbenoid insertion into a1 ,2-thiaborole,g enerating the 1,2thiaborine in relatively low yields. [21] Notably,t his complex features ad iisopropylamino group on the boron atom and exhibits as hort BÀNb ond of 1.407 ,i ndicative of as ignificant BÀN p-interaction that inevitably diminishes endocyclic participation of the boron p-orbital, hence, disruptingt he aromaticity.…”

“…[14,20,21] The synthetic methodology to prepare 3 involved ac arbenoid insertion into a1 ,2-thiaborole,g enerating the 1,2thiaborine in relatively low yields. [21] Notably,t his complex features ad iisopropylamino group on the boron atom and exhibits as hort BÀNb ond of 1.407 ,i ndicative of as ignificant BÀN p-interaction that inevitably diminishes endocyclic participation of the boron p-orbital, hence, disruptingt he aromaticity. Disorder in the solid-state structure, specifically with the carbon and sulfur atoms adjacent to boron,p reventeda na ccuratea nalysis of the endocyclic metricalp arameters.…”

Construction of Boron-Containing Aromatic Heterocycles

“…In 2011, the Ashe group reported the first synthesis of 1,2-thiaborinine by a similar synthetic procedure to that for 1,2-oxaborinine (Scheme 119). 178 Treatment of 2-(diisopropylamino)-2,5dihydro-1,2-thiaborole (432) with two equivalents of LDA in THF followed by reaction with excess dichloromethane gave 435. The proposed mechanism involves intermediate 434 formed via attack at C(3) of 433 by the in situ generated chlorocarbene, which was confirmed by control reaction employing deuterated dichloromethane.…”